Posttraumatic Stress Disorder (PTSD) is the product of traumatic stress operating on individual diatheses that span the spectrum of human variation in vulnerability to psychopathology. This interaction yields extensive phenotypic heterogeneity in samples of individuals with PTSD, one manifestation of which is a severe and diverse pattern of diagnostic comorbidity with commonly co-occurring disorders ranging from those of the internalizing spectrum (i.e., the unipolar mood and anxiety disorders) to the externalizing spectrum (i.e., antisocial behavior, the addictions, and disorders of impulse control). Dr. Miller's research program is focused on understanding the influence of enduring, temperament-based propensities towards internalizing and externalizing behavior on the form and expression of posttraumatic psychopathology. Through a series of studies, he and his colleagues have found evidence of internalizing and externalizing subtypes of PTSD across genders and trauma types. He has recently extended this work using confirmatory factor analysis and biometric twin modeling to implicate a genetic basis for the internalizing and externalizing dimensions underlying these subtypes. One limitation of work thus far has been a reliance on cross- sectional datasets and the resulting inability to evaluate the stability of the typology over time or the transactional relationships that likely exist between class membership and life stress. Therefore, the proposed study will conduct four- (Time 2) and six-year (Time 3) follow-up assessments of veterans who recently completed extensive assessments for Dr. Miller's prior Merit Review-funded study The Structure of PTSD Comorbidity. The study will also include assessment of new onset life stressors occurring between Time 2 and 3 to examine the stress- generative effects of internalizing and externalizing psychopathology as well as the symptom exacerbating effects of such stressors. This intensively-assessed sample of veterans offers a unique opportunity for longitudinal examination of a broad array of psychiatric symptoms and modeling influences on their trajectories.